Experimental Study On Mechanics Effects Of Fly Ash Soil Improved By Rubber Patricles Under Freeze-thaw Cycle

With the fast development of economy, the role of road transport is more and moreimportant and its influence on the national economy is growing. Seasonal frozen soil inChina is widely distributed throughout more than10provinces in the north of the YangtzeRiver, taking up53.5%of the country's total area. Road damage in seasonal frozen soil areais mostly caused by frost heave and frost boiling, which reduce the mechanical propertyindex of seasonal frozen soil. Improving the stability of roadbed in seasonal frozen soil areaand enhancing its freezing-thawing resisting characteristics as well as reducing freezinginjury are of great value to ensure the long-term safety operations of road in seasonal frozenarea.In this paper, freezing issues in seasonal frozen soil area are discussed based on theNational High Technology Research and Development Program (863Program)-"Technologycontrol study on roadbed resisting freezing-thawing stability", relying on G102nationalhighway expansion engineering projects. Meanwhile, the theory and application research onrubber particles modified fly ash soil under freeze-thaw cycles is carried out in this paper,with the main research work below:The rubber particles modified fly ash soil static properties are studied based on theexisted research results. By unconfined compressive strength tests, the frost resistance testand insulation test, we proposed fly ash soil mixtures (1:2) with2%rubber particles as coldresistance materials for roadbed in seasonal frozen soil areas. Laboratory tests proved thatrubber particles modified fly ash soil has properties of high compressive strength, smallamount of frost heave and good insulation.1. By using dynamic three axis test, and through the comparison of the dynamicparameters between rubber particles modified fly ash soil and pure fly ash soil, and theanalysis of the change law of these two materials' dynamic strength as well as dynamicmodulus under different confining pressures, we concluded that under the same confiningpressure, the dynamic strength of rubber particles modified fly ash soil and pure fly ash soilis inversely proportional to the damage circle number, while under the same damage circlenumber, the dynamic strength is proportional to the confining pressure, with the initialtangent modulus of rubber particles modified fly ash soil lower than pure fly ash soil as well as the average dynamic modulus larger than the unmodified fly ash soil.2. By using roadbed material mechanical parameters testing machine developed byResearch Group, we carried out the freezing-thawing tests of rubber particles modified flyash soil mixture. Under dynamic loading, we analyze the evolutionary process of themechanical properties in the process of freezing and thawing, and obtained the variation lawof mechanical index with positive and negative temperature as well as its relationship withFreezing and thawing cycles. By monitoring the temperature change inside the material, wecame to the evolutionary process between Mixture temperature and stress and strain whenthe outside temperature was changing.3. By analyzing the monitored stress data and strain data, we concluded that dynamicstress reduced with the decrease of temperature, and at the time of temperature changingbetween the positive and negative direction, there was a sudden decrease change for thedynamic stress. The first four dynamic stresses of freezing-thawing cycles decreased slightlybut the amplitude was small. And after5~8freezing-thawing cycles, the dynamic stresstended to be stable. Dynamic strain fell as the temperature decreased. The first four strainvalue decreased with freezing-thawing cycles increasing. But since the fifthfreezing-thawing cycle, the dynamic strain changed a little and tended to be stable. Dynamicmodulus of every circle was always maintained in a stable value. When the temperature wasreduced to a certain extent, dynamic modulus would no longer change. With the samefreezing-thawing cycle but different temperature, the dynamic modulus of rubber particlesmodified fly ash soil increased with the temperature increasing but the added value wassmall. When the temperature was the same but the freezing-thawing cycles was different, thedynamic modulus of rubber particles modified fly ash soil tended to be stable after3~8times.4. In order to further verify the road performance of fly ash soil improved by rubberparticles and explor the popularization and application of road construction in seasonalfrozen soil, we establish an1000m long experimental path on national highway G102line.We pave three different subgrade test sections and bury temperature sensor in thecenter,the top and bottom of the road at three roadbed filler layer. Then we collect thetemperature data of the roadbed filler at different location in different temperatureperiod.Analysis result shows that the rubber particles improved fly ash soil has low thermalconductivity and good thermal insulation performance.5. On the basis of FEM thermal analysis theory, subgrade temperature field of fly ash soil, the rubber particles modified fly ash soil and silty clay is studied.An subgradedimensional finite element model with insulating layer is established.Using this model,wemonitor parameters of subgrade frozen deep, the temperature gradient freeze of threeroadbed filler.Then we obtain the conclusion as follows: the temperature of the bottom ofinsulating layer is the highest on rubber particles improved fly ash soil.The insulating layerhas the minimum road freeze depth and the maximum temperature gradient; Silty clay acrossthe stratosphere has the maximum to freeze depth and the minimum temperature gradient. Atthe same time, we determine the minimum filling thickness of the rubber particles improvedfly ash soil. This minimum filling thickness can insure the roadbed is under a state ofpositive temperature.